* Add Floyd-Steinberg grayscale dithering.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2637 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/Makefile.am

@@ -29,6 +29,7 @@ libpipi_la_SOURCES = \
 	test.c \
 	$(codec_sources) \
 	filter/blur.c \
+	dither/floydsteinberg.c \
 	$(NULL)
 libpipi_la_CFLAGS = $(codec_cflags)
 libpipi_la_LDFLAGS = $(codec_libs) \

pipi/dither/floydsteinberg.c

@@ -0,0 +1,68 @@
+/*
+ *  libpipi       Proper image processing implementation library
+ *  Copyright (c) 2004-2008 Sam Hocevar <sam@zoy.org>
+ *                All Rights Reserved
+ *
+ *  $Id$
+ *
+ *  This library is free software. It comes without any warranty, to
+ *  the extent permitted by applicable law. You can redistribute it
+ *  and/or modify it under the terms of the Do What The Fuck You Want
+ *  To Public License, Version 2, as published by Sam Hocevar. See
+ *  http://sam.zoy.org/wtfpl/COPYING for more details.
+ */
+
+/*
+ * floydsteinberg.c: Floyd-Steinberg dithering functions
+ */
+
+#include "config.h"
+#include "common.h"
+
+#include "pipi.h"
+#include "pipi_internals.h"
+
+pipi_image_t *pipi_floydsteinberg(pipi_image_t *src)
+{
+    pipi_image_t *dst;
+    pipi_pixels_t *srcp, *dstp;
+    float *srcdata, *dstdata;
+    int x, y, w, h;
+
+    w = src->w;
+    h = src->h;
+
+    srcp = pipi_getpixels(src, PIPI_PIXELS_Y_F);
+    srcdata = (float *)srcp->pixels;
+
+    dst = pipi_new(w, h);
+    dstp = pipi_getpixels(dst, PIPI_PIXELS_Y_F);
+    dstdata = (float *)dstp->pixels;
+
+    for(y = 0; y < h; y++)
+    {
+        for(x = 0; x < w; x++)
+        {
+            float p, q, e;
+
+            p = srcdata[y * w + x];
+            q = p < 0.5 ? 0. : 1.;
+            dstdata[y * w + x] = q;
+
+            e = p - q;
+            if(x < w - 1)
+                srcdata[y * w + x + 1] += e * .4375;
+            if(y < h - 1)
+            {
+                if(x > 0)
+                    srcdata[(y + 1) * w + x - 1] += e * .1875;
+                srcdata[(y + 1) * w + x] += e * .3125;
+                if(x < w - 1)
+                    srcdata[(y + 1) * w + x + 1] += e * .0625;
+            }
+        }
+    }
+
+    return dst;
+}
+

pipi/pipi.h

@@ -67,6 +67,7 @@ extern pipi_image_t *pipi_gaussian_blur(pipi_image_t *, float);
 extern pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *,
                                             float, float, float, float);
 
+extern pipi_image_t *pipi_floydsteinberg(pipi_image_t *);
 extern void pipi_dither_24to16(pipi_image_t *);
 
 extern void pipi_test(pipi_image_t *);